Combined erasing and recording magnetic transducer



July 5, 1949.

M. CA COMBINED ERASING AND RECORDING MAGNETIC TRANSDUCER Filed May 30,1945 .F] g. I

TO OSCILLA OUTPUT 7 INPUT Marvin C'a'm rvrs TO AMPLIFIER Patented July5, 1949 COMBINED ERASING AND RECORDING MAGNETIC TRANSDUCER MarvinCamras, Chicago, Ill., assignor to Armour Research. Foundation of.Illinois Institute oi. Technology; a corporation of Illinois ApplicationMay 30, 1945, Serial No. 596,779.

3"Claims. 1

The present invention relates to. a magnetic recording and reproducingdevice, and more particularly to a specific construction thereof forincluding a recording gap and an erase gap in the same recording head,and in some instances, thev addition of a pick-up gap, also.

The term recording head-as .used in-the present specification andclaimsrefers; to an electromagnetic head for recording, reproducing orboth recording and reproducing.

Magnetic recordingheads comprise generally an electromagnet withopposingpoles, the edges of which are centrally grooved for accommodating anaxially movingparamagnetic wire which is incrementallymagnetizedlongitudinally in accordance with variations impressed on theelectromagnet coil by sound waves falling on a microphone. A commonmethod of operating a magnetic recording device is to first impress therecord on the longitudinally travelling wire by the recording head,afterwards to reproduce the record on the same or a different head andthen when desired, to erase or demagnetize the record by passing theWire througha separate erasing head, such as one energized by, highfrequency current. The provision of such separate erasing and recordingheads makes the apparatus cumbersome and relatively expensive tomanufacture.

An objectv of the present invention is to'comblue the erasing andrecording gaps in a single magnetic recording head, that is, in a singleelectromagnet, thereby simplifying the apparatus and making it lessexpensive to manufacture.

A more specific object of the present invention is to provide anelectromagnetic recording head embodying three separate gaps, namely, arecording gap, an erase gap, and a pick-up gap.

Other objects and advantages will become apparent from a study of thefollowing specification taken with the drawings wherein:

Figure 1 is a front view of a magnetic recording head embodying eraseand rewarding gaps in accordance with the principles of the presentinvention;

Figure 2 is a cross-sectional view taken along line IIII of Figure 1showing the central groove for guiding a longitudinally movingparamagnetic wire; and

Figure 3 is a modified magnetic, recording head embodying, in additionto the erase and recording gaps, a pick-up gap as well.

Referring more particularly to the drawings, numeral I generally denotesa magnetic recording head comprising a substantially E-shaped magneticcore 2, preferably of material of high magnetic permeability and lowretentivity. The outer legs 3 and 4 of the E-shaped core have laterallyinward extensions so as to present narrowly'tapered poles which are inconfronting relationship with the poles disposed on opposite surfaces ofthe end of the central leg of the E-shaped structure, thereby providingan erase gap 5'which may be of the order of 0.01 inch, and a recordinggap 6 which may be of the order of 0.002 inch. A low impedance erasecoil l is Wound on leg 3 and has a few number of turns such as, forexample,.20, whereas a somewhat higher impedance recording and pick-upcoil 0 is wound on leg 4, such coil having a relatively large number ofturns, such as, for example, about 2000. A few of the turns 9 of the lowimpedance coil 1 are Wound about leg 5, thereby threading the recordingside of. the electromagnet to provide a high freduencycomponent thereto.

Figure 3 shows a modified form of recording head similar to that shownin Figure 1 except that there is added an additional pick-upelectromagnet having a substantially U-shaped' core l2 on one of whichlegs is wound a high impedance pick-up coil it. An advantage of makingthe pick-up coil of high impedance isthat it elimihates the necessityfor an input transformer which transformer not only addsto the expenseand complication of the appara-tusbut introduces distortion. A pick-upgap 20 is provided between the ends of core l2. Core i2 may be eitherWelded or merely placed in close abutting relationship with a projectingportion M of the substantially E-shaped core 15. On one leg of the E-shaped core I5 is wound a low impedance erase coil l6 and on the otherleg, a low or medium impedance recording coil i! so as to provide anerase gap l0 and recording gap i9, respectively. An advantage of makingthe erase or recording coil of low or at least medium impedance is thatit will facilitate winding of the coils and coupling to associatedcircuits. While cores l2 and I5 may be made of the same material, it ispreferable to make them of diiierent materials because the desiredcharacteristics of the pick-up head and recording head are somewhatdifferent. More specifically, core l2 of the pick-up head should havehigh initial permeability because the flux threading the pick-up coildepends upon the permeability of the magnetic circuit, and shouldenerate the least amount of noise when the wire :00 passes through thecentral groove H on playaok.

While turns 9 are shown below coil 8 of Fig. 1 and will! of Fig. 3, itshould be notw. that in some cases better operation is obtained if theyare placed above these coils. On the other hand, core 15 of therecording head and erase head should be of material that does notsaturate readily, because it is undesirable to have the core materialsaturate before the wire saturates. Wires have saturation values of theorder of 8000 to 20,000 lines per square centimeter depending on thewire materials whereas the above mentioned alloys have higher saturationvalues although their initial permeability is lower than that ofMu-metal.

It should be noted that separate magnetic paths exist for each of thecoils and their associated gaps. For example, the erase coil provides aflux which extends through the leg which it surrounds as well as acentral part of core l whereas the recording coil l'l provides a fluxgoing through its supporting leg and the central leg of core l5, and thepick-up coil l3 has induced a flux which extends through both legs ofthe U-shaped core I 2 traversing pick-up gap 20.

If desired, the E-shaped structure shown in Figure 1 or 3 may besubdivided vertically in two halves as illustrated, that is, may be madeup of two separate cores having adjoining surfaces such as the surfacesexisting between the E-shaped and U-shaped cores of Figure 3.

The open design provided by the E-shaped structures permits insertion orremoval of wire without threading. Thus, it will be seen that I haveprovided an eilicient multipurpose electromagnet including not only arecording gap but an erase gap and in some instances a pick-up gap aswell, thereby providing a relatively compact structure for accomplishinga number of purposes in a magnetic recording device.

It will, of course, be understood that various details of constructionmay be varied through a wide range without departing from the principlesof this invention and it is, therefore, not the purpose to limit thepatent granted hereon otherwise than necessitated by the scope of theappended claims.

I claim as my invention:

1. A magnetic recording head comprising a magnetic core having aplurality of legs, a relatively low impedance coil mounted on one legand a relatively high impedance coil mounted on another leg, the ends ofsaid legs being in closely spaced relationship to form two non-magneticgaps energized by a different one of said coils, and means for guiding amagnetic record member along a path substantially parallel to themagnetic axes of said gaps and successively across said gap.

2. A magnetic recording head comprising a flat magnetic core including aplurality of legs forming a plurality of aligned gaps and having arelatively low impedance coil mounted on one leg and a relatively highimpedance coil mounted on another leg, the ends of said legs havinglateral extensions projecting in closely spaced relationship withopposed end portions of a centrally disposed leg to form an erase gapenergized substantially only by said low impedance coil and a recordinggap energized by said high impedance coil, said legs including means forguidin a magnetic record member along a path substantially parallel tothe magnetic axes of said gaps and successively across said gaps.

3. A magnetic recording head comprising a substantially E-shapedmagnetic core having a relatively low impedance coil mounted on oneouter leg and a relatively high impedance coil mounted on the otherouter leg, the ends of said outer legs being in closely spacedrelationship with the end portion of the center leg to form twonon-magnetic gaps, said low impedance coil having a pair of leadsthrough which said coil is energized by a high frequency source, one ofsaid leads making several turns around said other outer leg adjacentsaid high impedance coil to provide a high frequency component.

MARVIN CAMRAS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,815,010 Pollock July 14, 19312,351,011 Camras June 13, 1944 FOREIGN PATENTS Number Country Date805,434 France Nov. 19, 1936

